1. Field of the Invention
The present invention relates generally to photolithographic methods and mask devices that are utilized for multiple exposures of photoresist in the field of a feature, such as the placement of an identification number on a device such as a slider for a magnetic head.
2. Description of the Prior Art
When devices are created on a wafer substrate, such as a slider including a magnetic head or other microelectronic devices, an identification number is typically created on each such device. In the past, the identification number has been written on the back side of the slider using a laser etching technique. However, flash (ablated particulates) on the back side of the wafer due to the laser serialization of the sliders can result in the redeposition on the front side of the ablated material from the site of the characters formed on the back of the slider. This etching created flash can be deleterious to hard disk drive performance because it is a source of contamination that can lead to device failures, such as HDI's (head disk interactions), e.g. head crashes.
Moreover, as the dimensions of sliders move to the “femto” format, back side serialization of the slider necessitates the flipping of sliders over for inspection of slider identifiers in the serialization pattern. Since the small size of these sliders raises problems with regard to handling, it is desirable to serialize the front side of the wafer to avoid the handling that accompanies flipping these small format sliders over for inspection of slider identifiers.
More recent prior art slider serialization methods are based on photolithographic techniques that use mask sets to print row and column identifiers of sliders, as well as wafer identification numbers on individual sliders. However, these other methods, such as are described in U.S. Pat. Nos. 6,897,010 and 6,924,090, require significant processing time and are therefore costly. The methods and mask sets described in this invention provide a novel approach to front side serialization that brings substantial cost savings. Moreover, the invention may have many fundamental and novel applications outside of the particular embodiments recited with regard to wafer serialization when the invention is applied to the art of photolithography more generally.